Apparatus and method for edge grinding of plates



' B. D. ROBBINS March 18, 1958 APPARATUS AND METHOD FOR EDGE GRINDING 0F PLATES 4 Sheets-Sheet 1 Filed Nov. 1, 1954 I INVENTOR Bruce DJZobbzn/s ATTORNEY March 18, 1958 B. D. ROBBINS APPARATUS AND METHOD FOR EDGE GRINDING 0F PLATES Filed Nov. 1. 1954 4 Sheets-Sheet 2 INVENTOR fj'ruce DJZobb ins ATTORNEY March 18, 1958 I B. D. ROBBINS 2,326,372

APPARATUS AND METHOD FOR EDGE GRINDING OF PLATES Filed NOV. 1, 1954 4 Sheets-Sheet 3 INVENTOR Bruce DJZobbin/s ATTORNEY 1 March 18, 1958 B. D. ROBBINS 2,826,372

APPARATUS AND METHOD FOR EDGE GRINDING 0F PLATES Filed Nov. 1, 1954 2 4 Sheets-Sheet 4 INVENTOR" Bra/cc flRabbin/s ATTORNEY Patented Mar. is, was

APPARATUS AND METHOD FGR EDGE GRINDING 0F PLATES Application November 1, 1954, Serial No. 465,8

8 Claims.

This invention relates to improvements in the method of and apparatus for grinding and finishing the peripheral edge of plates, such as plates or panes of shatterproof glass that are used in the windows of automobiles.

More particularly the invention relates to apparatus for and method of applying pressure to the finishing wheel throughout certain portions of its contact with the edge of such plates so that a highly polished edge is obtained. For example, in the automobile door windows the side edges and the bottom do not require the high degree of polish as the normally exposed upper edge or top edge of the glass plate.

The invention is illustrated by a particular machine similar to that shown in Patent 2,080,280, issued May 11, 1937, but may be applied to other grinding machines.

In grinding the peripheral edge of glass plates, such as window plates for automobiles, the plates are chucked up and rotated about a center of rotation. A main grinding wheel grinds the peripheral edge in accordance with a given pattern and a finishing wheel effects a finishing polish thereafter. These glass plates are usually of nonuniform shape having curved and linear portions. The finishing wheel or grinder yieldingly contacts the peripheral edge and where the portions of the edge of the glass plate are radially closer to their center of rotation, the

polishing wheel does not apply the same pressure that it does on a more radially remote edge from the center of rotation. Thus, it may be that the edge which is radially closer to the center of rotation of the plate requires a higher degree of polish as it may be the exposed edge of the glass plate When in use. Such is the case with automobile door window panes.

The primary object of my invention is to control the pressure applied to the finishing wheel such that a greater pressure is applied in certain selected edge portions where the plate of glass will be exposed so that a higher degree of polish is obtained.

A further object of my invention is to control the application of this pressure to the finishing Wheel in a certain selected synchronism of rotation with the rotating plate.

A still further object of my invention is to speed up the operation of dressing the peripheral edges of plates by carrying out the finished polishing of the edge at a rate not less than the grindingof the edge by the main grinding wheel.

A still further object of my invention is to provide apparatus which will apply additional pressure to the finishing wheel along certain selected portions of the edge of a plate.

Another object of my invention is to provide a cylinder and piston power unit which is connected with the finishing wheel and control apparatus such that the power unit applies pressure to the finishing wheel in certain selected areas of its contact with the peripheral edge of the glass plate being dressed.

Yet a still further object of my invention is to provide a cylinder and piston power unit, a spring coupling between the power unit and the finishing wheel, a con-' trolled fluid pressure supply for applying pressure to the power unit and cam means for controlling the fluid pressure supply to the power unit which cam means is rotated in synchronisrn with the rotation of the plate whose edge is being dressed.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific example is given by way of illustration only and, while indicating preferred embodiments of the invention are not given by way of limitation, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

For a more complete understanding of the nature and scope of my invention, reference may be had to the following drawings in which:

Fig. 1 is a side elevation of a glass plate edge grinding machine having the pressure applying apparatus for the finishing wheel applied thereto according to my invention;

Fig. 2 is a top plan view along section line 22 of Fig. 1 showing the front portion of the apparatus in Fig. l with the rear portion broken away;

Fig. 2a is an enlarged detail view of the finishing grinding wheel and cam follower associated therewith as viewed along section lines 2a-2a of Fig. 2;

Fig. 2b is an enlarged side elevation of the cam follower mounted on the pivoted arm carrying the main grinding wheel as viewed along section lines 2b2b of Fig. 2;

Fig. 3 is an enlarged top plan view of the auxiliary pressure applying apparatus for the finishing wheel as shown in Fig. 2 but with the right-hand portion broken away;

Fig. 4 is a side, elevation of the auxiliary pressure applying apparatus along section line 4-4 of Fig. 3;

Fig. 5 is an end elevational view along section line 5-5 of the auxiliary pressure applying apparatus as shown in Fig. 4;

Fig. 6 is an enlarged side elevation of the split cam controlling the microswitch for the pressure applying valve;

Fig. 7 is a sectional view along line '7-7 of Fig. 6 showing the split cam;

Fig. 8 is a diagrammatic side elevation showing the main dressing wheel and the relative positions of the finishing wheel and control cam closing the microswitch;

Fig. 9 is a View similar to Fig. 8 but with the plate rotated counter-clockwise and the finishing wheel at its extreme right-hand position with microswitch about to be opened by the cam;

Fig. 10 is a side elevation similar to Figures 8 and 9 but showing the glassplates still further rotated counterclockwise with the control cam opening the microswitch; and

Fig. 11 is an enlarged'diagrammatic side elevation in section of the three-way pressure control valve for the power applying unit.

Throughout the various views and description like reference numerals refer to similar parts.

Figure l shows a typical plate glass'edge grinding ma.-

chine generally indicated at it? having a base frame ill,

a centrally disposed plate rotating shaft 12 mounted in the support frame 7.1 and having a drive gear 13 driven through speed reduction gearing generally indicated at 14. Chuck mountings for the glass plates A and 13V are generally indicated at 15. The speed reduction gearing 14 is driven by a motor 16 through a belt drive 1'7 lead- 7 ing to pulley 18. Pulley 13 is inountedon a counter shaft 18 that also mounts a drive sprocket 19 which l 3 drives the control cam generally indicated at and described hereinafter. The glass plates A and B mounted in their chucks 15 are rotated at a relatively slow speed by the motor 16 and through the speed reduction gearing 14. Plates A and Blie in a common plane with their grinding wheels to be described.

Referring to Fig. 2, there is mounted behind plates A and B cam plates or patterns A and B which are actually cams. These cam plates A and have the outer peripheral configuration of the final size of glass plates A and B. In Fig. 2b a cam follower 21 for the main grinding wheel 27 is adjustably mounted by adjusting bracket 22 and shaft 23 with bracket 22 being mounted on the pivot arm 24. Arm 24 as shown in Fig. 1 is pivotally mounted at 25 and is counterweighted by counterweight 26. This arm 24 carries the main grinding wheel 27 which is driven through a belt generally indicated at 28 by a motor 29 mounted above counterweight 26, all of which is typical apparatus. Referring back to Fig. 2b, shaft 23 which mounts the cam follower 21 on adjustable bracket 22 may be adjusted by the adjusting screw 22'. This cam follower 21 follows the cams A and B and being mounted on the arm 24 controls the positioning of main grinding wheel 27 which makes the first grinding cut on the plates A and B as they rotate counter-clockwise against the counter-clockwise rotating main grinding wheel 27. Each of the grinding wheels 27 and 37 has a grooved periphery that contacts the edges of the glass plates.

In Fig. I mounted on the right-hand of the frame 11. is an upstanding pivotal -arm Mon a pivot shaft 31 trunnioned in frame 11. i This upstanding pivot arm 36 carries a drive motor 32 and at the upper end a transverse shaft 33 on which is mounted a pulley 34 which is driven through a belt 35 leading to a pulley 36 on motor 32.- Reference to Fig. 2 shows shaft 33 having mounted thereon a grinding wheel 37 which is grooved and is termed the finishing or trailing wheel. Surrounding the grinding wheel 37, see Figures 1 and 2a, is a shroud or guard 38 which is mounted on upstanding arm 30.

Mounted on this guard 38 in an adjustable manner by means of guides 3939 is a cam followerdll. This cam follower 40 is supported on another shaft 41 mounted in slide 42 which slides in the guideways 39-39. Guideways 39-39 have a transverse end joined thereto as at 43 which is threaded and receives an adjusting screw 44 that moves the slide 42 and the shaft 41 to position the cam follower 40. Cam follower 40, see Fig. 2, cooperates with the cams or cam plates A and B so as to guide or limit the inward movement of the trailing or finishing wheel 37.

In Fig. 1 as well as in Figures 8-10 it will be observed that a chain 45 attached at one end to the upstanding pivot arm 30 mounting trailing wheel 37 is led over an idling sprocket 46 attached to frame 11 and has its depending end 45 secured to a counterweight 47. This counterweight 47 acting through the chain 45 yieldably presses the trailing wheel 37 against the peripheral edge of plates A and B as they come in contact therewith. This trailing wheel 37 is in fact the finishing wheel which puts on the finishing grind on the edge of the glass plates A and B. It will be observed in all of the figures that trailing wheel 37 rotates counter-clockwise. This is typical apparatus to hold the usual finishing or trailing wheel 37 in contact with the edge of the glass plates A and B.

It will now be observed by reference to Figures 8-10 that plate A is a typical window glass plate for an automobile door and its upper or exposed edge when in use in the door is indicated as a, the two ends are b and b and the bottom isindicated at c. It is desired to place a satin finish onthe upper exposededge a as well as the rounded corners a and a". In Fig. 8 it will be observed that the finishing wheel 37 is in contact with edge a which edge is radially closer to the center of rotation, the

4 shaft 12, of plates A and B than is the corner a" as shown in Fig. 9 which is in contact with the grinding wheel 27. The normal pressure in this typical apparatus is effected through the counterweight 47 as shown in Fig. 1 attached to chain 45 leading to pivotal arm 30. Of necessity, when the plate A rotates as shown in Fig. 9 in a counter-clockwise direction corner a" is farther away or removed from the center of rotation 12 and thus the finishing wheel 37 is pivoted to the right and greater pressure is applied. However, it is desired along the edge a that a greater pressure he applied so as to grind a satin finish. It is the purpose of applicants invention to provide a method and apparatus for applying pressure to the grinding wheel 37 in this selected zone along edge a or other selected zones to effect a satin finish.

To accomplish this, applicant provides a novel auxiliary pressure-applying apparatus and a method of controlling and applying same to the selected edge portion or portions. In Fig. 1 a power producing unit generally indicated at 50 comprises a cylinder 51 having a piston and piston rod 52 operating therein. This cylinder 51 is adjustably mounted, see Fig. 2, in a channel shaped trough 53 supported in a horizontal attitude on the frame support 11 of the grinding machine. This U-shaped trough 53 has formed in the upstanding sides thereof a plurality of spaced apart through apertures 54 :which receive a securing pin 55 as best shown in Fig. 2.

Reference to Fig. 5 shows the U-shaped trough 53 and the apertures 54 and the rear or left end of the bracket 56 attached to the cylinder 51. Bracket 56 is generally square in shape and forms a hearing which rides in the trough 53. A bracket 57 is attached to the bearing end 56 of piston 51 by means of screws 58 and has a rearwardly or leftwardly extending strap 59 whose end is apertured and received by the securing. pin 55 in an ad justed position in one of the apertures 54. Bracket 57 has forwardly extending bifurcated ears 5757' which are apertured and have attached thereto coil springs 60-60 which extend to the right and are attached at their opposite ends to a transverse bar or cross head 61 pivotally attached by a pivot pin 62 to a clevis 63 fastened on the end of piston rod 52. Each end of the transverse cross head 61 on the end of piston rod 52 has apertures 61' which receive the ends of the springs 69-60 and a pair of additional springs 64-64 of the coil type which have extreme ends at the right hooked onto the links of chains 45 as indicated at 64'. The adjustment feature of the power unit 50 in trough 53 is to provide for larger plates of glass. Also adjustment of tension in the springs 60 and 64 may be effected by adjusting the position of power unit 50. The ends of springs 64 may be adjustably positioned along chains 45. While referring to Fig. 3 it will be noted that a bearing 65 is attached to the frame 11 by means of a bracket support 66 and screws 67 to support a shaft 46. which shaft carries the idling sprockets 46-46 on the ends thereof over which the tension chains 45 are trained.

Referring to Fig. 1, the piston and cylinder unit 5! or power producing unit is supplied fluid pressure through a flexible connection 67 attached to a hose connection 51" at the right end of the cylinder. Flexible hose 67 is connected to a fluid pressure power line generally indicated at 68 which is supported by bracket 69 and leads downwardly through the grinding machine to a power source (not shown) at the left lower corner of the ma chine. This pressure line 68 is of normal construction and has a pressure regulator 69, a filter 70, a relief valve 71, a pressure indicating gauge 72, and a three-way con trol valve generally indicated at 73.

. Valve 73 is a combination cut-off and vent valve and is shown diagrammatically in Fig. 11. It is powered by a solenoid S and has a housing 74 with air supplied thereto at the top through the pressure supply line 68. In the position shown the valve is venting the pressure cylinder 50 through the passages X and Z by the reciprocating valve stem 75. Stem 75 is biased in a left or venting position by means of spring 76 secured thereto by washer 77 and a cap screw 78. When solenoid S is energized the valve stem 75 is pulled to the right, closes passage Z and opens passage X to the interior of the valve housing and to the passage Y at the supply line thus permitting fluid pressure to be applied to the cylinder 51 to move the piston and piston rod 52 to the left. The power operated three-way valve 73 which has a solenoid S is further controlled by means of the microswitch 80 which has an operating arm 81 with a roller 82 on the end thereof which contacts cams generally indicated at 29. Microswitch 80 is in an electrical power supply line 83. The other side of the power supply line 84 leads from the solenoid S to a power source (not shown) adjacent the bracket 69.

In Fig. 6 the microswitch 8 h is shown in more detail and has an arm operator 80 which is actuated by the plunger 81. Referring to Fig. 6 and Fig. 7, the control cam generally indicated at 20 is of the split cam type having a first part or plate 120 with a collar 120 which is attached by set screw 121 to a countershaft 122 sup ported by an upstanding bracket 123. Adjacent plate 129 is a second plate 124 which has an arcuate slot 124 therein which receives a securing screw 125 anchored in the first plate 12%. Each of the cam plates 120 and 124 has oppositely disposed dwells 120 and 120' for plate 129 and similar dwells for plate 124 which are shown in overlapped positions in Fig. 6. Thus, by easing up on screw 125, plate 124 may be adjusted angularly with respect to plate 120 so as to increase or decrease the length of the dwell. Extending across the dwell of both cam plates is the roller 82 on pivot arm 81 which operates the plunger 80 of microswitch 80.

Referring again to Fig. 1, it will be observed that countershaft 122 carrying cam 20 also carries a sprocket 126 which is coupled by a chain 127 to sprocket 19 on the reduction gear shaft 18. The drive shown is a one to one ratio and thus as the plates A and B are rotated about their mounting and axis of rotation 12, sprocket 126 is likewise rotated in unison or synchronism so that the cam generally indicated at 29 rotates at the same speed as the plates A and B are rotated.

Again referring to Figures 8-10 and the positions of the cam 26, it will be noted that when the roller 82 is in the dwell of cam 2t switch 84 is closed and completes the circuit to solenoid S which actuates the three-way valve 73. Pressure is applied to the power unit 50, namely, the cylinder 51 which moves the piston rod and piston 52 to the left as shown in Fig. 8, thus applying a pressure through the springs 6% to pull or exert pressure on the grinding'wheel 37 through its pivotal arm 30. This takes place as the grinding wheel is in contact with the edge a of plate A and likewise a similar edge on plate 3 when it is rotated counter-clockwise into contact position. This additional pressure effects the satin finish which. is desired on this particular edge; It will be noted in Fig. 9 that the plates A and B have rotated counter-clockwise such that the corner a has come into contact with wheel 37 and cam 20 has rotated so that the cam roller 32 is at the end of the dwell and rising so as to cut off microswitch 80 and interrupt the circuit to the solenoid S. This permits the spring 76 of the valve generally indicated at 73 to take over and move the valve stem to the left, close off the pressure and open up the flexible supply line 67 to the atmosphere to vent the cylinder. As this occurs the springs 64 will take over and pull the piston and rod 52 to the right, as best shown in Fig. 10.

Advancing now to Fig. 10, the roller 82 has followed along the high point of the cam 2d and maintains the microswitch 80 open and no additional pressure is applied along the edges b and b of the lower corners c' and c" of plate A in this particular set up. However,

it is entirely feasible if found necessary for other shapes springs permit application of pressure to finishing wheel 37 without shock. V V

In carrying into practice my invention, I provide the tension spring elements 60-60 between the cross head 61 and the cylinder 51 and the further spring elements 64-6 5 between the cross head 61 and the chains 45-45 which apply a force on the pivot arm 30 supporting the grinding wheel 37. This arrangement of the spring elements assures that when power is applied to the power unit 50 to apply auxiliary pressure on the grinding wheel 37, such application of power is cushioned by these spring elements, particularly elements -64, so that the wheel 37 does not damage the edges of glass plates A and B.

This auxiliary pressure applying apparatus is positive in operation and through the split cam 20 adjustment can be made so that pressure is applied in selected areas of other shapes of glass plates than A and B being edge ground.

By my method of applying auxiliary pressure to the normally yieldable grinding wheel for edge finishing of plates such as glass, the speed of grinding of the main grinding wheel 27 in such machines is not impaired. While I have illustrated my method of applying auxiliary pressure as carried out by a particular machine and by a particular apparatus, this method is equally as well applicable in other grinding operations.

I claim as my invention: g

1. An apparatus for finishing the edges of glass plates, including a plate support that is rotatable on an axis normal to the plate body, and a rotating grinding wheel that is yieldingly supported and that yieldingly engages the edge of the rotating plate; the improvement of an auxiliary pressure applying apparatus for applying increased pressure on said grinding wheel in its engagement with said plate edge at selected portions only, comprising, a power unit having a force applying output means, a spring connected between said force applying output means of said power unit and said grinding wheel to provide a yielding coupling whereby any chatter between said grinding wheel and the plate is eliminated, power supply means for said power unit, and control means connected intermediate said power unit and said power supply means to supply power to said power unit, said control means including a rotatable cam rotated in synchronism with said rotatable plate support and including a sharply cut-out portion, a cam follower for said cam, said cam follower being operatively connected with said control means to apply and cut off the power supply to said power unit at selected stages of rotation of said plate in said plate support, thereby causing said grinding wheel to contact said plate edge with suddenly increased pressure at selected edge portions to apply a higher degree of ,finish in such edge portions than in other portions of the plate.

2. An apparatus for finishing the edges of plates, including a plate support that is rotatable on an axis normal to the plate body, and a rotating grinding wheel that is yieldingly supported and that yieldingly engages the edge of the rotating plate, said plate having a portion of its edge radially closer to its axis of rotation than another portion thereof; the improvement of an auxiliary pressure applying apparatus for applying increased pressure on said grinding wheel in its engagement with said plate edge portion radially closer to said axis of plate rotation, comprising, a piston and cylinder power unit arranged to apply a pulling force, pull applying coupling means including a tension spring connecting said power unit and said grinding wheel for applying pressure to said grinding wheel, said power cylinder and tension spring working together to apply a pulling force to said grinding wheel in its engagement withsaid plate, fluid pressure supply means connected with said power unit, and control means connected intermediate said fluid pressure supply and said power unit to apply fluid pressure to said cylinder and piston power unit when said grinding wheel is contacting the edge portion of said plate at said edge portion thereof radially closer to the center of rotation of the plate and cutting off the fluid pressure from said supply to said power unit when the grinding wheel contacts said edge portion of the ,plateradially more removed from the center of rotation ofsaid plate.

3. An apparatus for finishing the edges of plates, including aplate support that is rotatable on an axis normal to the plate body, and a rotating grinding wheel that is yieldingly supported and that ,yieldingly engages the edge of the rotating plate, said plate having a portion of its :edge radially closer ,to its axis of rotation than another portion thereof; the improvement of an auxiliary pressure applying apparatusfor applying increased pressure on said grinding Wheel for its engagement with said plate edge portion radially closer .to said axis of plate rotation, comprising, a power unit having a pulling force producing output means, coupling means including a tension spring connecting said power unit output means and said grinding wheel forapplying the combined pulling force of said power unit and said tension spring to said grinding wheel, power supply means for said power unit, and control means connected intermediate said power unit and said power supply means to supply power to said power unit to apply increased pressure to said grinding wheel when it is contacting the edge portion of said plate at said edge portion thereof radially, closer to the center of rotation of the plate and cutting oifthe power supply to said power unit when the grinding wheel contacts said edge portion of the plate more removed from the center of rotation of said plate.

4. An apparatus for finishing the edges of plates, including a plate support that is rotatable on an axis normal to the plate body, and a rotating grinding wheel that is yieldingly supported and that yieldiugly engages the edge of the rotating plate, said plate having a portion of its edge radially cioser to its axis of rotation than another portion thereof; the improvement of an auxiliary pressure applying apparatus for applying increased pressure on said grinding wheel for its engagement with said plate edge portion radiallycloser to said axis of plate rotation, comprising, a piston and cylinder power unit, spring means connecting said piston and said grinding wheel and acting in the same direction in cooperation with said power unit for applying pressure to said grinding wheel in its contact with said plate and minimizing shock between the grinding wheel and plate when pressure is applied, fluid pressure supply means, valve means having a solenoid actuator connected intermediate said fluid pressure supply and said power unit and including a vent for venting said cylinder, and control: means for said valve for opening same to apply pressure to said power unit when said grinding Wheel is contacting the edge portion of the plate that is radially closer to the center of rotation of the plate and closing same and opening the vent to said powerunit when said grinding wheel is contacting the edge or" the plate more removed radially from the center of rotation of the plate, said control means comprising a rotatable cam, means for rotating said cam in synchronism with, said plate, switch means operable by said cam and connected in an electrical power source to energize and deenergize said valve actuating solenoid.

5. An apparatus for finishing the edge of plates, in-

8 eluding a plate support that is rotatable on an axis normal to the plate body, and a rotating grinding wheclthat is yieldingly supported and that yieldingly engages the edge of the rotating plate; the improvement of an auxiliary pressure applying apparatus for applying increased pressure on said grinding wheel in its engagement with said plate edge at selected portions only, comprising, a piston and cylinder power unit, tension spring means connecting said piston and said grinding wheel for applying pressure to said grinding wheel and minimizing shock between the grinding wheel and plate when pressure is applied, an adjustable mounting for said piston and cylinder power unit on said apparatus for moving the power unit toward or away from said grinding wheel, fluid pressure supply means for said power unit, valve means having a solenoid actuator connected intermediate saidlluid pressure supply and said power unit and including a vent for venting said cylinder, and control means for said valve for opening same to apply pressure to said power unit when said grinding wheel is contacting the edge portion of the plate where a greater degree of polish is desired and relieving said pressure in other portions of said edge, said control means comprising a rotatable cam, means for rotating said cam in synchronism with said plate, switch means operable by said cam and connected in an electrical power source to energize and deenergize said valve actuating solenoid in step with the relation of said plate and cam to apply and remove increased pres sure between said grinding wheel and plate at selected edge portions.

6. An apparatus for finishing the edge of plates, in cluding a plate support that is rotatable on an axis normal to the plate body, and a rotating grinding wheel that is yieldingly supported and that yieldingly engages the edge of the rotating plate; the improvement of an auxiliary pressure applying apparatus for applying increased pressure on said grinding wheel in its engagement with said plate edge at selected portions only, comprising, a

piston and cylinder power unit, said piston having a piston rod connected thereto, a cross head fixed to the end of said piston rod, tension spring means connecting said cross head and cylinder, adjustable mounting means for said power unit on said apparatus for moving the power unit toward or away from said grinding wheel and comprising a U-shaped channel member which forms a trough to slidably receive said piston and cylinder power unit, said channel member having its upstanding sides provided with spaced apart oppositely disposed apertures therealong, a removable pin received in a selected pair of opposed apertures and strap means connecting said cylinder and said pin, said grinding wheel having a pivoted arm support, a weighted chain means attached to said pivot arm support of the grinding wheel and yieldingly holding said grinding wheel in contact with the edge of said plate, means connecting said crosshead and said weighted chain leading to said grinding wheel and including a tension spring for applying pressure to the grinding wheel and minimizing shock between the grinding wheel and plate when pressure is applied, said last mentioned connecting means, fluid pressure supply means for said power unit, valve means having a solenoid actuator connected intermediate said fluid pressure supply and said power unit and including a vent for venting said cylinder, and control means for said valve for opening same to apply pressure to said power unit when said grinding wheel is contacting the edge portion of the plate where a greater degree of polish is desired and relieving said pressure in other portions of said edge, said control means comprising a rotatable cam, means for rotating said cam in synchronism with said plate, switch means operable by said cam and connected in an electrical power source to energize and deenergize said valve actuating solenoid in step with the rotation of said plate and aaaas'rz cam to apply and remove increased pressure between said grinding wheel and plate at selected edge portions.

7. The method herein described which comprises sustaining a rapidly rotating polishing wheel in contact with the edge of a non-circular glass plate including a pair of corners and a side edge interconnecting the corners,

slowly rotating the plate through the point of contact thereof with the polishing wheel, and in the course of such operation suddenly increasing the pressure of contact of the polishing wheel with the edge of the plate as a corner of said pair of corners passes the point of contact, maintaining the increased pressure while the pair of corners and interconnecting side edge pass the point of contact, and suddenly decreasing the pressure of contact of the polishing wheel with the edge of the plate as the other corner of said pair of corners passes the point of contact thereby effecting a higher degree of polish of said edge at said portion where said grinding wheel contacts said edge portions of the plate with an increased pressure.

8. The method herein described which comprises sustaining a rapidly rotating polishing wheel in yielding con- 10 tact with the edge of a non-circular glass plate including a pair of corners and a side edge interconnecting the corners, slowly rotating the plate through the point of contact thereof with the polishing wheel, maintaining a relatively fixed first pressure of contact between said wheel and edge of the plate, and in the course of such operation applying an additional pressure independent of the first source on said wheel in its contact with said edge as the pair of corners and interconnecting side edge pass the point of contact thereby effecting a higher degree of polish of said edge portion in such selected areas than in the other edge portion.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,826,872 March 18, 1958 Bruce D. Robbins It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 27, for "relation" read rotation Signed and sealed this 21st day of October 1958.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Conmissioner of Patents 

